I'd say see an endocrinologist first based off your age. Symptoms such as having issues losing excessive belly fat, a lack focus, or feeling lethargic. Can be linked to testosterone levels. No, getting on test is not necessarily the answer, but knowing your test and estrodial levels are pretty important when you're 35+. You can supplement D3 to raise your test levels naturally which would help with burning fat during workouts. Naturally is a very difficult process as you'd have to 40,000-100,000 iu of D3 daily if you wanted to naturally raise your levels. Medical studies show that it is safe to take 100,000 iu per day (during a 1yr study) when raising men's test levels without injecting Testosterone Cypionate. Yes, dieting and excerise will play a huge factor but it's an uphill battle with age if you're no longer harmonally balanced.
If you don't care to see where you are harmonally, you can try hopping in a BodPod, learning what your body is actually metabolizing, then building a diet and workout plan around that.
Having belly stick out is a common problem for thos who wants to remodel their silhouette. There are couple things that helped me (I'm still working on my belly, but results are visible). Start with determining why your belly is not flat. Is it because of fat (this is my case and in fact most common one), or maybe there is some other factor at play here. If it is because of fat - start by reducing your daily calories intake - 200 to 400 less kcal a day will force your system to use the fat that it has stored. Depending on your fitness level - excercise. Start by going for walks - an hour a day will do. For excercises - try light excercises with some resistance (two small water bottles'll do as dumbells for starters), or calisthenics (push ups, pull ups, squats, sit ups, glute bridges). You should also look at your daily habits. Having a beer at evening, or when whatching a game on TV will set you back a lot! Look through Grokker videos library for excercise ideas. Just avoid everything that says HIIT, or High Intensity Interval Training. You'll get ther later on your fitness journey.